I had a chat with a certain very well known fiddle player with hearing loss (and behind the ear aids) a couple of months ago. He said "You'll have to speak up, I can't hear you." So I just pulled one aid out of my ear & said "Makes two of us!" Arf arf.   

I did a bit more research about the Bluetooth device from Siemens which I could use with my new aids. It's a MiniTek, and is really a streamer. When your phone rings, the call is routed to the hearing aid(s) via MiniTek. You can also get TV sound, digital stereo etc routed to the aids, there's a telecoil (eg for use in a theatre), and even an FM adaptor at even more cost.

The downside is that although the caller can be heard on your hearing aids, your voice also goes via the Minitek which is round your neck, on your lapel or in your pocket with the Polos, flat picks & fluff! I can imagine the person at the other end getting some interesting results unless you speak right into the thing, in which case you might blow their eardrums out.

Anyway, inveterate techies may like to have a look......
http://hearing.siemens.com/Global/en/products/wireless/minitek/minitek.html